A modern motor vehicle powered by an internal combustion engine is equipped with an engine control module (ECM) for controlling various engine operational parameters such as spark timing, fuel injection, valve timing, emission controls, and so on. The algorithms for carrying out these control functions are based in part on current atmospheric conditions such as ambient air pressure and temperature, and measures of these and other parameters are ordinarily obtained from discrete sensors. In certain instances, the sensors can be mounted on a circuit board within the ECM to minimize system cost, but parameters such as ambient air pressure cannot be reliably sensed inside the ECM, particularly in applications where the housing of the ECM is environmentally-sealed. Accordingly, the ambient air pressure is ordinarily measured with a wired external sensor coupled to the ECM via its wiring harness. For reduced system cost, however, it would be desirable to obtain a reliable measure of ambient air pressure while avoiding the increased expense associated with a wired external sensor.